Thermal fatigue in solder joints of Ag-Pd and Ag-Pt metallized LTCC modules

The fatigue behaviour of joints between ceramic LTCC modules and FR-4 board s was investigated using thermal cycling tests at temperature intervals of 0 degreesC - 100 degreesC and -40 degreesC - 125 degreesC and analysis of t he cycled modules using scanning acoustic microscopy and SEM/EDS. The assem blies were fabricated with Ag-Pd and Ag-Pt metallized pads on LTCC. Fatigue cracks initiated in the solder region of the Ag-Pd metallized LTCC modules , but propagated later in the ceramic module. Propagation was remarkably re tarded by Ag-filled vias located under the pads on LTCC. The final cracks t hat caused an electrical failure in the modules crossed the root region of the vias along the thick Ag3Sn+PdSn4 layer located in this region. The join ts of the Ag-Pt metallized modules passed the resistance measurement in bot h tests. However, they also showed crack growth that initiated on the LTCC/ metallization interface, propagated in the ceramic, but was retarded by the vias. These vias were resistant to fracture, since only a thin Ag3Sn layer (approximate to 1 mum) existed in their root region. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.